Biosynthesis of Plant-derived flavor
compounds
By Dudsadee Uttapap
References
1. “Flavor Chemistry and Technology”, H.B. Heath, G. Reineccius, 1986.
2. “Flavor Chemistry”, D.B. Min, http://class.fst.ohio-state.edu/fst820/default.htm
3. “Biosynthesis of plant-derived flavor compounds”, The Plant
Journal (2008) 54, 712–732
4. “Plant Biochemistry” http://www.uky.edu/~dhild/biochem/lecture.html
Biosynthesis of plant-derived flavor compounds
Flavor compoundsFlavor compounds
Flavor molecules constitute a heterogeneous group of compounds, with straight-chain, branched-chain, aromatic and heteroaromatic backbones
bearing diverse chemical groups such as hydroxyl, carbonyl, carboxyl, ester, lactone, amine, and thiol functions. More than 700 flavor chemicals h
ave been identified and catalogued
Chemical synthesis VS Chemical synthesis VS BiosynthesisBiosynthesis
Most commercial flavorants are ‘nature identical’, which means that they are the chemical equivalent of natural flavors but are chemically synthesized, mostly from petrol
eum-derived precursors
Bioproduction, including the extraction from natural sources, de novo microbial processes (fermentation), and bioconversion of natural precursors using micro-organisms or isolated enzymes
Biological functions of plant volatilesBiological functions of plant volatiles
Compounds emitted by flowers most probably serve to attract and guidCompounds emitted by flowers most probably serve to attract and guide pollinators e pollinators
volatiles might also protect the carbohydrate-rich nectar by inhibiting mivolatiles might also protect the carbohydrate-rich nectar by inhibiting microbial growth.crobial growth.
vegetative plant tissue release volatiles following herbivore damage. vegetative plant tissue release volatiles following herbivore damage. Some of these substances attract arthropods that prey upon or Some of these substances attract arthropods that prey upon or
parasitize the herbivores. parasitize the herbivores. Volatiles also act as direct repellents or toxicants for herbivores and Volatiles also act as direct repellents or toxicants for herbivores and
pathogens.pathogens.In fruits, volatile emission and accumulation facilitate seed dispersal by In fruits, volatile emission and accumulation facilitate seed dispersal by
animals and insects.animals and insects.vegetative tissues often produce and release many of the vegetative tissues often produce and release many of the
volatiles after their cells are disrupted. These volatile flavor volatiles after their cells are disrupted. These volatile flavor compounds may exhibit anti-microbial activity.compounds may exhibit anti-microbial activity.
““associated with defensive and attractive rolesassociated with defensive and attractive roles””
Aromatic compounds responsible for od or and flavor of fruits comprise;
Alcohols
Carbonyls
Acids
Esters
Lactones
Phenols
R-OH
R-CHOR-CO-R’
-R COOH
- -R COO R’
R
O CO
Estimated Estimated world world
consumption consumption of selected of selected
aroma aroma chemicals in chemicals in
flavor and flavor and fragrance fragrance
compositionscompositions
CHO
OH
OCH3
Calvin cycle
N enters roots as NO3- or NH4+. The NH4+ is incorporated into amino acids in roots and leaves and the amino acids accumulate in proteins. The main if not sole function of some proteins is to provide a store of amino acids
Amino acid synthesis
Amino acid synthesis
Glycolysis
isoprenoid biosynthesis proceeds either via the "classical" or most well studied, mevalonate pathway (cytosolic) (for the synthe
sis of sterols, sesquiterpenes, triterpenoids)
or via the non-mevalonate (1-deoxy-D-xylulose-5-phosphate, DXP) pathway for plastidic isoprenoids (carotenoids, phytol [side-chain of chlorophylls], plastoquinone, isoprene, monoterpenes a
nd diterpenes).
Biosynthesis of flavors in vegetables an d fruits
develop when tissue damage occurs
(Intact vegetable generally contains few volatiles)
Vegetable flavors
are formed during brief ripening period
Fruit flavors
Minute quantities of lipids, CHO, protein (amin o acids) are enzymatically converted to volatile fl
avors.
BIOGENESIS OF FRUIT AROMA
develops entirely during ripening period of plant
FRUIT FLAVOR COMPOUNDS
AppleApple n-hexanal, ethyl butyrate, 1-propyl n-hexanal, ethyl butyrate, 1-propyl propionate, 1-butyl acetate, trans-2-propionate, 1-butyl acetate, trans-2-hexenal, ethyl 2-methylbutyrate, 2-hexenal, ethyl 2-methylbutyrate, 2-methylbutyl acetate, 1-hexanol, hexen-methylbutyl acetate, 1-hexanol, hexen-1-ol, trans-2-hexen-1-ol, hexyl acetate, 1-ol, trans-2-hexen-1-ol, hexyl acetate, Esters; alcohols; aldehydes; ketone; Esters; alcohols; aldehydes; ketone; acids; including hexanal; ethyl 2-acids; including hexanal; ethyl 2-methyl butyrate methyl butyrate
BananaBanana alcohols; esters, including amyl acetate, alcohols; esters, including amyl acetate, isoamyl acetate, butyl butyrate, amyl b isoamyl acetate, butyl butyrate, amyl b ut yr at e ut yr at e
PeachPeach - -Ethyl acetate, dimethyl disulfide, cis 3 - -Ethyl acetate, dimethyl disulfide, cis 3 hexenyl acetate, methyl octanoate, eth hexenyl acetate, methyl octanoate, eth
- yl octanoate, 6 pentyl alpha pyrone, ga - yl octanoate, 6 pentyl alpha pyrone, ga mma decal act one mma decal act one
Lipids Polysaccharide Proteins/Enzymes Lignins
Aliphatic Terpenes Methyl-Branched AromaticAcidsAlcoholsEstersCarbonylslactones
SesquiterpenesHydrocarbonsAlcoholsCarbonylsmonoterpenes
AlcoholsAcidsEsterscarbonyls
AlcoholsAcidsEsterscarbonyls
Biosynthesis of fruit volatiles
Carbohydrate Amino
acid
Cinnamicacid
Terpene
Fattyacid -AcetylCoA
MalonylCoA Acetyl C
oA
Pyruvate
MevalonylCoA
Shikimic acid
Flavorants from carbohydrate metabolism
Furanones and pyrones
“fruit constituents”
O nly a limited number of natural vol atiles originate directly from carboh
ydrates without prior degradation of the carbon skeleton.
Furanones and pyrones
- - - -4 25Carbohydrate derived flavor molecules, including hydroxy , di- - - - - - -ff3 (2 ) ( ), 2 ,5 4 3 ( 2 )
- - - - - 4 5 32ranone (methoxyfuraneol), hydroxy methyl ( H) furanone (nor - - - - - - - 2 4 5 32furaneol), ethyl hydroxy methyl ( H) furanone (homofurane
- - - - - - - 4 2 5 32ol), hydroxy methylene methyl ( H) furanone (HM M F) and- - - - - - - 3 2 4 4hydroxy methyl H pyran on (maltol).
Glycolysis
Glucose (6C)
2 Pyruvate (3C)
Ethanol LactateTCA Cycle
CO2
+O2
-O2 -O2
Flavorants from carbohydrate metabolism
Pyruvic acid CH3COCOOH
Acetic acid CH3COOH
Acetyl CoA CH3COSCoA
+ CO2
Malonyl CoA HOOCCH2COSCoA
Malonic Acid HOOCCH2COOH
“ the most interesting is terpene biosynthesis”
Terpenoids are enzymatically synthesized from acetyl CoA and pyruvate provided by the carbohydrate pools in
plastids and the cytoplasm.
Terpenoids constitute one of the most diverse families of
natural products, with over 40 000 different structures of
terpenoids
Many of the terpenoids produced are non-volatile and are involved in important plant processes such as membrane
structure (sterols), photosynthesis (chlorophyll side chains, carotenoids), redox chemistry (quinones ) and growth
regulation (gibberellins, abscisic acid, brassinosteroids)
Flavorants from carbohydrate metabolism
Important plant-derived volatile terpenoids.
Biosynthesis of Terpenes
“ -isoprene is derived from acetyl CoA”
Classification of Terpenes
Apocarotenoid formationApocarotenoid formation
Carotenoid substrates are oxidatively cleaved to yield the apocaroten oid derivatives (right).
Some of the volatile organic compounds in wine come from the grape's skin, or exocarp, while others come from the grape's flesh, or mesocarp. Organic acids give wine its tartness, and sugars give it sweetness. Terpenes provide floral or fruity flavors. Norisoprenoids impart a honeylike character. Thiols are the sulfur-based
compounds behind complex wine aromas such as guava, passionfruit or grapefruit — but when thiols go wrong, they can make a wine taste "funky."
products; acids, alcohols, diketones, ketones, esters of these compounds.
Lipids
metabolic pathway for lipid biosynthesis plays a significant role in flavor formation.
Alpha-, -Beta oxidation
Oxidation via lipoxygenase
Lipoxygenase activity is believed to be the major source of volatiles in plants.
Oxidation via Lipoxygenase
Major products : volatile C6 and C9 aldehydes and alcohols
Substrate : unsaturated fatty acid ( linoleic and linolenic acids).
Lipoxygenase enzymes (dioxygenase) catalyze reactions between O2 and polyunsaturated fatty acids
- Linolenic acid derived flavor molecules.
AAT, al cohol acyl CoAt ransf erase ; ADH, al cohol dehydrogenase; AE R, alkenal oxidoreductase; AOC, allene oxide cyclase; AOS, allene oxi
de synthase; HPL, hydroperoxide lyase; JMT, jasmonate methyltransferase; LOX, lipoxy
- - - -genase; OPR, 12 oxo phytodienoic acid reductase; 3Z,2E EI, 3Z,2E e nal isomerase.
Fatty acid precursors (Tomato)
- and -oxidation of fatty acids
- Palmitoyl CoA (1 6 :0 )
- Myristoyl CoA (1 4 :0 )
+ Acetyl-CoA
the specific pathways in plants are not well understood
-Formation of pear flavors via beta oxidation
Lactones
Amino Acid Metabolism
Amino acid metabolism yields short chain aliphatic and aromatic alcohols, acids, carbonyls and esters
They are the primary source of branched chain aliphatic flavor compounds
their pathways have been barely analyzed in plants.
amino acid precursors(Tomato)
- (a) Catabolism of branched chain amino acids leading to methyl branched f lavor compounds, and (b) postulated biosynthesis of sotolon. Formation of
aldehyde (a) from amino acids requires the removal of both carboxyl and a mino groups. The sequence of these removals is not fully known and could b
e the opposite to that shown or aldehyde could be formed in one step by ald ehyde synthase
- Biosynthesis of amino acid derived flavor compounds
Starting amino acids: Tyrosine and phenylalanine products: phenolic/spicy in character
Shikimic acid formation
Vegetable Flavors
Vegetable flavors
- flavor again arises from major metabolic processes e.g. Lipids, CHO & amino acids.
The role or importance of S compounds to v egetable flavor is quite significant.
the precursors, enzymes and end flavors are quit e different from fruits.
Nonvolatile PrecursorsLinoleic, Linolenic acid Thioglucosinolates Cysteine-sulfoxides Methyl-methionine
Precursor-splitting EnzymesLypoxygenase Thioglucosidases C-S-lyases None (Heating)
CarbonylsAlcoholsOxo-acids
IsothiocyanatesNitrilesS C OThiocyanates
PolysulidesAlkyl-thosulfinates
CH3-S-CH3
Carbohydrate
Fatty acid Amino acid
Formation of flavor in vegetables
Vegetable Flavor Categories
Genus Allium
Enzymes produce volatiles from derivatives of cysteine (sulfoxides)
Genus Brassica
Enzymes produce volatiles from glucosinolates
Alliaceous vegetables
garlic ( Allium sativum L.)
onion ( Allium cepa L.)
chive ( Allium schoenoprasum L.)
leek ( Allium porrum L.)
Characteristic flavors
not exist in the bulb before processing
are produced when the cellular tissues are ruptured by cutting or chewing
flavor is produced very rapidly by the action of an enzyme on the odorless precursors wh ich coexist in the cells
Onion and Garlic Flavor
Enzymatic reaction of cysteine derivative
Glucosinolate precursors are important to the flavor of both the Brassica and Cruciferae fami
ly
Cruciferae family includes radish, horseradish,mustard.
GLUCOSINOLATES
thiocyanate, nitrile, or isothiocyanate
& glucose
Hydrolysis of the glucosinolate
glucosinolate
thioglucosidase
Natural carbon pools for the Natural carbon pools for the productionproduction
of flavor compounds, and the of flavor compounds, and the pathwayspathways
Mevalonic acid Acetate Mevalonic acid
Isoprene
Shikimic acid Pyruvate + Erythrose phosphate
“ the most interesting is terpene biosynthesis”
most of essential oils get flavor from terpenoids (10 carbon)
- Limonene a monoterpene hydrocarbon - is the major terpene in many or most citrus products. Orange > 95% of the essenti al oil is limonene,
lemon ~ 65% limonene, yet is of little flavor significance.
- Citral oxygenated monoterpene - seldom comprises > 2% - of the essential oil of lemon largely carries the lemon flavo
r.
Flavorants from carbohydrate metabolism
1 Methane 1 Methane 11 Undecane 11 Undecane 2 1 Henicosane 2 1 Henicosane 31 Hentriacont 31 Hentriacontaneane
2 Ethane 2 Ethane 12 Dodecane 12 Dodecane 22 Docosane 22 Docosane 32 Dotriaconta 32 Dotriacontaffff
3 Propane 3 Propane 13 Tridecane 13 Tridecane 23 Tricosane 23 Tricosane 33 Tritriaconta 33 Tritriacontaffff
ffffff4 ffffff4 14 Tetradecan 14 Tetradecanff 24 Tetracosane 24 Tetracosane 40 Tetracontan 40 Tetracontan
ff
fffffff5 fffffff5 15 Pentadecan 15 Pentadecanff
25 Pentacosan 25 Pentacosanff
50 Pentaconta 50 Pentacontaffff
6 Hexane 6 Hexane 16 Hexadecan 16 Hexadecanff 26 Hexacosane 26 Hexacosane 60 Hexacontan 60 Hexacontan
ff
7 Heptane 7 Heptane 17 Heptadecan 17 Heptadecanff
27 Heptacosan 27 Heptacosanff
70 Heptaconta 70 Heptacontaffff
8 Octane 8 Octane 18 Octadecane 18 Octadecane 28 Octacosane 28 Octacosane 80 Octacontan 80 Octacontanff
f fffff9 f fffff9 19 Nonadecan 19 Nonadecanff 29 Nonacosane 29 Nonacosane 90 Nonacontan 90 Nonacontan
ff
10 Decane 10 Decane 20 Icosane 20 Icosane 30 Triacontane 30 Triacontane 100 Hectane 100 Hectane
Isoamyl acetate, a strong fruity odor described as similar to banana or pea
r - - 2 M ethyl butyl acetate has a strong a
pple scent